The invention relates to a drive system.
The invention also relates to a machine tool, production machine or a robot having the abovementioned drive system.
According to customary practice, machines, such as, for example, machine tools, production machines or robots, have a multiplicity of “machine axes”, the movements and positions of which are controlled by a controller, in particular a numerical control. An important factor in this case is, inter alia, exact guidance of the relative movement and the relative position between a spindle of the machine and the workpiece to be machined. Machining of the workpiece by the tool produces the desired contour on the workpiece. In the process, the drives of the individual machine axes must perform very exact traverse and rotary movements. In addition to rapid and precise axis drives, the productivity, for example of a machine tool, depends on a high spindle speed. The spindle has a spindle drive motor which normally forms a unit with a spindle rotor. The spindle drive motor sets the spindle rotor in rotation. Virtually all the spindles used at present have a mechanical bearing arrangement, e.g. in the form of a rolling element bearing arrangement. The disadvantages of the mechanical bearings at high speeds are generally known. In this regard, high wear of the mechanical bearings occurs at high speeds. Since the lubricant supply to the bearings is complicated, the disturbances frequently occurring in the lubricant supply lead to an often premature failure of the bearing. A further problem constitutes the residual unbalance of the spindle rotor. This occurs in interaction with the machine structure and causes pronounced vibrations and noise at certain speeds.
Wear and vibration behavior can be considerably improved through the use of a magnetically mounted spindle. In many cases, magnetic spindle bearing arrangements are used according to the prior art. The magnetic spindle bearing arrangement is a contactless system in which magnetic forces controllable via magnetic bearings assume the role of the rolling elements. The position of the spindle rotor is in this case measured continuously and the magnetic forces are always dynamically readjusted in such a way that the spindle rotor keeps the desired position in the bearing center even during loading.
Shown in FIG. 1 in a schematic illustration is a magnetic spindle bearing arrangement 23. It comprises a spindle rotor 10, which is mounted by means of magnetic bearings 11c, 11d, 11e, 11f and 11g (only shown schematically for the sake of clarity), and a performance module 16. Each magnetic bearing 11c, 11d, 11e, 11f and 11g essentially comprises an electromagnetic yoke which is fitted with coils and acts on the passive spindle rotor 10. In this case, the magnetic bearings 11e and 11f carry out the guidance in the X direction, the magnetic bearings 11d and 11g carry out the guidance in the Y direction and the magnetic bearing 11c carries out the guidance in the Z direction. Assigned to the magnetic bearings 11c, 11d, 11e, 11f and 11g are respectively associated distance sensors 12c, 12d, 12e, 12f and 12g which measure the distance from the spindle rotor 10 and feed respectively associated analog actual position signals 15c, 15d, 15e, 15f and 15g as input variables to a performance module 16. The performance module 16 comprises control devices 18c, 18d, 18e, 18f and 18g which act on the respectively associated magnetic bearings 11c, 11d, 11e, 11f and 11g via respectively associated power converters 17c, 17d, 17e, 17f and 17g and via respectively associated lines 8c, 8d, 8e, 8f and 8g. In this case, the control devices 18c, 18d, 18e, 18f and 18g and the power converters 17c, 17d, 17e, 17f and 17g need not necessarily be an integral part of the performance module 16, but may also be present as individual components. The control devices 18c, 18d, 18e, 18f and 18g are connected to the respectively associated power converters 17c, 17d, 17e, 17f and 17g for the exchange of data, which is indicated by double arrows in FIG. 1. The performance module 16 and the magnetic bearings 11c, 11d, 11e, 11f and 11g form a control loop which keeps the spindle rotor 10 floating.
Furthermore, a commercially available drive system of a machine, such as, for example, a machine tool, a production machine or a robot, is shown in FIG. 1. Via a data bus 2, of a two-axis machine in the example, a controller 1 is connected to a drive device 3a and 3b for activating the drive motors 7a and 7b and in particular to a control device 4a and 4b. The data communicated via the data bus 2 are, for example, speed, acceleration and position data of the individual drives. The control device 4a and 4b activates a respectively associated power converter 5a and 5b via a respectively associated connection 6a and 6b. The power converters 5a and 5b activate respectively associated drive motors 7a and 7b via respectively associated 3-phase lines 8a and 8b. In this case, each drive motor 7a and 7b activates a respective machine axis of the machine. A respective actual position encoder 12a and 12b is assigned to each drive motor 7a and 7b, an actual position signal 15a being fed as input variable to the control device 4a by the actual position encoder 12a and an actual position signal 15b being fed as input variable to the control device 4b by the actual position encoder 12b. In this case, each drive device comprises a control device and a power converter, although the control device and the power converter need not necessarily be accommodated in a common housing. The control device and power converter may also quite easily be in the form of separate components. The controller 1, for example, inputs position setpoints into the control device 4a and 4b via the data bus 2. The actual position values 15a and 15b are then controlled in accordance with the position setpoints input by the controller 1 and the machine axes are moved in this way.
As shown in FIG. 1, a commercially available drive system of a machine has no connection to the magnetic spindle bearing arrangement 23. The power converters 5a and 5b for activating the drive motors 7a and 7b are, as shown in FIG. 1, three-phase, whereas the power converters 17c, 17d, 17e, 17f and 17g of the magnetic spindle bearing arrangement 23 are only two-phase. For this reason, the drive devices, in particular the power converters 5a and 5b which serve to activate the drive motors 7a and 7b and the power converters of the spindle bearing arrangement, have hitherto not been regarded as being interchangeable. This results in considerable disadvantages with regard to maintenance of machines and the stockkeeping of spare parts for machines having a magnetic spindle bearing arrangement.
Furthermore, the actual position encoders 12a and 12b, according to customary practice, always deliver incremental actual position signals 15a and 15b, whereas the actual position encoders 12c, 12d, 12e, 12f and 12g of the magnetic spindle bearing arrangement 23 deliver analog actual position signals 15c, 15d, 15e, 15f and 15g. For this reason, the control devices 4a and 4b have hitherto not been regarded as being interchangeable with, for example, the control devices 18c and 18d of the performance module 16 for the magnetic spindle bearing arrangement. As with the power converters, this likewise has considerable disadvantages with regard to maintenance and stockkeeping of spare parts. In addition, due to the separation of the drive system and the magnetic spindle bearing arrangement 23, two different procedures for the drive devices 3a and 3b on the one hand and for the magnetic spindle bearing arrangement 23 on the other hand are to be taken into account during start-up.
As a result, the labor cost for start-up and maintenance is considerably increased. Since the control devices 18c, 18d, 18e, 18f and 18g of the magnetic spindle bearing arrangement 23 have no communication with the controller 1, the magnetic spindle bearing arrangement 23 also cannot be integrated in the motion guidance of the machine axes, e.g. for vibration damping.
Furthermore, a modern controller of a machine, in particular a numerical control, contains diverse diagnostic possibilities, extending right through to remote diagnosis via the Internet. However, since the magnetic spindle bearing arrangement 23, according to customary practice, does not communicate with the controller 1 via the data bus 2, it also cannot be included in the diagnostic possibilities already existing.